In this study, a dynamic cycle test, a static immersion method and a pyrolysis experiment were combined to examine the characteristics of SO42− released from several new and old cation exchange resins used in condensate polishing systems for power plants. The results show that the quantity and velocity of SO42− released from new and old resins tend to balance in a short time during the dynamic cycle experiment. SO42− is released by 1500H (monosphere super gel type cation exchange resins) and 001 × 7 (gel type cation exchange resins) new and old cation exchange resins, the quantity of which increases according to immersion time. In the pyrolysis experiment, the quantity of SO42− released from resins increases and the pH of the pyrolysis solution transforms from alkaline to acidic with an increase in temperature.